1. Field
The apparatuses and methods consistent with the present inventive concept relate to the transmission and reception of digital television (DTV) signals in over-the-air broadcasting, which DTV signals include robustly coded data and accompanying signaling designed for reception by mobile/handheld (M/H) receivers.
2. Related Art
The Advanced Television Systems Committee (ATSC) published its ATSC Digital Television Standard in 1995 as Document A/53, hereinafter referred to simply as “A/53” for sake of brevity. The Annex D of A/53 titled “RF/Transmission Systems Characteristics” is particularly incorporated by reference into this specification. A/53 describes vestigial-sideband (VSB) amplitude modulation of the radio-frequency (RF) carrier wave using an eight-level modulating signal, which type of over-the-air DTV broadcasting is called “8-VSB”. In the beginning years of the twenty-first century, efforts have been made by some in the DTV industry to provide for more robust transmission of data over broadcast DTV channels without unduly disrupting operations of so-called “legacy” DTV receivers already in the field. Robust transmission of data for reception by M/H receivers will be provided for in successive versions of an ATSC standard for DTV broadcasting to M/H receivers referred to more briefly as the M/H standard. An initial version is an ATSC Mobile DTV Standard referred to as “A/153” for sake of brevity. A/153 has been published by ATSC as a candidate standard.
The operation of nearly all legacy DTV receivers is disrupted if 2/3 trellis coding is not preserved throughout every transmitted data field. Also, the average modulus of the DTV signal should be the same as for an 8-VSB signal as specified in the 1995 version of A/53, so as not to disrupt adaptive equalization in legacy receivers using the constant modulus algorithm (CMA).
Another problem concerning “legacy” DTV receivers is that a large number of such receivers were sold that were designed not to respond to broadcast DTV signals unless de-interleaved data fields recovered by trellis decoding were preponderantly filled with (207, 187) Reed-Solomon (RS) forward-error-correction (FEC) codewords of a specific type or correctable approximations to such codewords. Accordingly, in order to accommodate continuing DTV signal reception by such legacy receivers, robust transmissions are constrained in the following way. Before convolutional byte interleaving, data fields should be preponderantly filled with (207, 187) RS FEC codewords of the type specified in A/53.
This constraint has led to M/H data encoded for reception by M/H receivers being encapsulated within (207, 187) RS FEC codewords of type similar to that specified in A/53. The (207, 187) RS FEC codewords differ somewhat, however, in that they are not necessarily systematic with the twenty parity bytes located at the conclusions of the codewords. The twenty parity bytes of some of these (207, 187) RS FEC codewords appear earlier in the codewords to accommodate inclusion of training signals in the fields of interleaved data. The 207-byte RS FEC codewords invariably begin with a three-byte header similar to the second through fourth bytes of an MPEG-2 packet, with a thirteen-bit packet-identification (PID) code in the fourth through sixteenth bit positions. (MPEG-2 packets and MPEG-4 packets are two types of data transport packets specified by the Moving Picture Experts Group.) Except for the three-byte header and the twenty parity bytes in each (207, 187) RS FEC codeword, the remainder of the codeword has been considered to be available for “encapsulating” 184 bytes of a robust transmission. (In actuality, the inventor notes, the last byte of the three-byte header of the 207-byte RS FEC codeword can also be replaced by a byte of M/H data, so a 207-byte RS FEC codeword could “encapsulate” 185 bytes of a robust transmission.)
A/153 specifies that successive equal lengths of M/H data streams are subjected to transverse RS (TRS) coding, and then, to periodic cyclic redundancy check (CRC) coding to develop indications of possible locations of byte errors in the TRS coding. These procedures are designed to correct byte errors caused by protracted burst noise, particularly as may arise from loss of received signal strength, and are performed in an apparatus called an “M/H Frame encoder”. An M/H Frame is a time interval that, at least usually, is of the same 968-millisecond duration as twenty 8-VSB frame intervals. The M/H Frame is sub-divided into five equal-length M/H sub-frames, each composed of 16 successive Groups of M/H data, thereby defining 80 Slots for M/H data in each M/H Frame. The related M/H data within a selected set of the 80 Slots in an M/H Frame is referred to as a “Parade”. Each Parade is composed of one “Ensemble” or of two Ensembles located in different portions of Groups. Each Ensemble is TRS and CRC coded independently of every other Ensemble.
The output signal from the M/H Frame encoder is supplied for subsequent serial concatenated convolutional coding (SCCC) of the general sort described by Valter Benedetto in U.S. Pat. No. 5,825,832 issued Oct. 20, 1998 and titled “Method and Device for the Reception of Symbols Affected by Inter-symbol Interface”. An encoder for the SCCC comprises an outer convolutional encoder, an interleaver for two-bit symbols generated by the outer convolutional encoder, and an inner convolutional encoder constituting the precoder and 2/3 trellis coder prescribed by A/53.
A/153 specifies that parity bytes generated by the TRS coding shall be transmitted at the conclusion of each of successive equal lengths of 187-byte M/H data streams used for generating them. TRS coding of M/H data frames extends over 968-millisecond intervals of 8-VSB signals. Three options are specified for the TRS coding. M/H transmissions shall use (211, 187), (223, 187) or (235, 187) TRS coding.
An initial portion of the TRS encoding procedure in the M/H Frame encoder can be analogized to a matrix-type block interleaving procedure of the following sort. A first RS framestore of the M/H Frame encoder is written row by row with respective successive equal lengths of M/H data stream, and then, read column by column to the RS coder, which generates successive TRS codewords. A final portion of the TRS coding procedure in the M/H Frame encoder can be analogized to a matrix-type block de-interleaving procedure of the following sort. A second RS framestore of the M/H Frame encoder is written column by column and row by row with respective to successive TRS codewords, and then, read row by row to reproduce respective successive equal lengths of the M/H data streams, each being followed by TRS parity bytes.
In an M/H receiver for M/H signals, turbo decoding of an SCCC'd M/H signal is followed by a TRS decoding and error-correction procedure. An initial portion of the TRS decoding procedure in an M/H Frame decoder can be analogized to a matrix-type block interleaving procedure of the following sort. A first RS framestore of the M/H receiver is written row by row with respective successive equal lengths of M/H data streams, each with TRS parity bytes, and then, read column by column to the RS decoder, which generates successive corrected TRS codewords. A final portion of the TRS decoding procedure in the M/H Frame decoder can be analogized to a matrix-type block de-interleaving procedure of the following sort. A second RS framestore is written column by column and row by row with respective corrected TRS codewords, and then, read row by row to reproduce respective successive equal lengths of error-corrected M/H data streams. The second RS framestore of the M/H receiver can be smaller than the first RS framestore since only data bytes of the corrected TRS codewords need to be subjected to the block de-interleaving procedure.
It takes 968 milliseconds for an RS framestore in the M/H receiver for M/H signals to be fully written, so TRS decoding and error-correction can begin. It then takes some time for the TRS decoding and error-correction to proceed and for subsequent block de-interleaving to be done. After this, block de-interleaved corrected M/H data can be written into a first-in/first-out (FIFO) cache memory that supports operations of subsequent stages of the receiver. Some time is necessary for the FIFO cache memory to fill sufficiently that there is little chance for the subsequent stages of the M/H receiver to be starved for bits required for their operation. The foregoing procedures introduce a delay of two seconds from the time a baseband M/H signal is received to be available for the M/H signal, as corrected by TRS decoding procedures, to be available for processing by later stages of the M/H receiver using a real-time transport protocol (RTP). This delay affects the time taken to change sub-channel selection if all available sub-channels are not being concurrently processed, presuming that an RF channel change is not required. If an RF channel change is required there will be further time required for re-tuning and stabilization of a front-end of the M/H receiver that heterodynes the M/H signal transmissions to the baseband and equalizes a channel response, which further time is typically only a fraction of a second.
The time for change in sub-channel selection set forth in the previous paragraph presumes that the change is made just previously to the beginning of an M/H Frame. If the M/H Frame has already begun when the change in sub-channel selection is made, there will be a wait until a next M/H Frame begins. That is, supposedly, only data the TRS decoding procedures find to be correct will be passed on to later stages of the M/H receiver. A/153, the candidate standard published in 2009, was based on a document submitted to the ATSC by LG Electronics Co., Ltd. on Oct. 15, 2007, which document is titled “MPH Physical Layer Technical Disclosure”. The LG Electronics' M/H transmission system as originally proposed is designed to transmit an MPEG-2-compatible stream of 187-byte transport packets. However, it was decided by an ad hoc group within ATSC to transmit indeterminate-length Internet-Protocol (IP) Transport Stream (TS) packets instead. The indeterminate-length IP packets cannot be parsed by simply referring to the beginnings of rows of bytes in a TRS frame. Accordingly, A/153 prescribes that each of the rows of bytes in TRS frames begin with a 16-bit, two-byte header that includes an indication of where in the row an IP packet begins, if an IP packet begins in that row and is the first IP packet to begin in that row. If more than one IP packet begins in a row, the beginning of each further IP packet is reckoned from packet length information contained in a header of a preceding IP packet. The header of each IP packet contains a 16-bit, two-byte checksum for CRC coding of that particular IP packet.
An IP signal supplied to later stages of an M/H receiver includes Service Map Table-mobile/handheld (SMT-MH) packets transmitting a respective SMT for each Ensemble included in M/H signal transmission. These SMT-MH packets are used for assembling an Electronic Service Guide (ESG) that is made available on a view screen for guiding a user of the M/H receiver in the user's selection of a sub-channel to be received and a mode of reception of that sub-channel. After such selection by the user, stored SMT-MH data is used for conditioning an operation of the M/H receiver accordingly. Each SMT-MH packet includes indications therewithin as to whether the SMT-MH packet repeats a previous SMT-MH packet for the Ensemble or updates the previous SMT-MH packet. The repetition of SMT-MH packets is designed to make available an additional degree of protection of SMT-MH data against corruption by noise.